<template>
  <div>
    <ul class="list">
      <li class="item"
          v-for="item in letters"
          :key="item"
          :ref="item"
          @touchstart.prevent="handleTouchStart"
          @touchmove="handleTouchMove"
          @touchend="handleTouchEnd"
          @click="handleLetterClick">
        {{ item }}
      </li>

    </ul>
  </div>
</template>

<script>
export default {
  name: 'cityAlphabet',
  props: {
    cities: Object
  },
  computed:{
    letters(){
      const  letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  data() {
    return {
      touchStatus: false,
      startY:0,
      timer:null,
    }
  },
  updated() {
    this.startY = this.$refs["A"][0].offsetTop
  },
  methods: {
    handleLetterClick(e) {
      this.$emit('change', e.target.innerText)
      // console.log(e.target.innerText)
    },
    handleTouchStart() {
      this.touchStatus = true
    },
    handleTouchMove(e) {
      if(this.touchStatus){
        if(this.timer){
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(()=>{
        const touchY = e.touches[0].clientY -79
        const index = Math.floor((touchY - this.startY) / 20)
        if(index >= 0 && index < this.letters.length){
          this.$emit('change', this.letters[index])
        }
        },5)
      }
    },
    handleTouchEnd() {
      this.touchStatus = false
    },
  }
}
</script>

<style lang="stylus" scoped>
@import "~styles/varibles.styl"
.list
  display flex
  flex-direction column
  justify-content center
  position absolute
  top 1.58rem
  right 0
  bottom 0
  width .4rem

  .item
    line-height .4rem
    text-align center
    color $bgColor
</style>
